Mozilla Firefox has been listening to recent memory complains, and as a side effect tested the browser's scalability to the extreme with memshrink's improvements.
The results are shocking: For 150 tabs open using the test script, Firefox nightly takes 6 min 14 on the test system, uses 2GB and stays responsive. For the same test, Chrome takes 28 min 55 and is unusable during loading. An optimized version of the script has been made for Chrome as an attempt to work-around Chrome's limitations and got an improved loading time of 27 min 58, while using 5GB of memory.

Firefox is eventually moving to a multi-process architecture a la Chrome (though that's probably still 6 months away). So for sure Mozilla agrees that's the better approach. But notice that not even Chrome can rely on that for security, since above a certain number of open tabs, multiple tabs end up sharing the same process. I also wouldn't say that "threads are an optimization, that's all". Threads are light-weight processes, i.e. processes that share the same address space.

actually its such statements that lead to incomprehension.
multiprocess is not technically the better solution but its the one that works best in practice, because it provides a higher isolation.

thats why chrome works well. its actually a pretty crappy browser in SOME regards. it crashes a lot, its quickly slowing down, etc
since its multiprocess it doesnt matter too much, everything is working properly again as soon as you close the tab

current firefox cannot do that. it cannot afford anything going wrong because resetting things back means restarting the complete browser